An aerial vehicle, such as a missile, projectile or unmanned aerial vehicle (UAV), typically is launched from either a tube or a rail. Such a vehicle is very difficult to launch ballistically (i.e. without wings functioning as primary lifting surfaces), and then later in the flight to deploy wings that can function as primary lifting surfaces for non-ballistic flight.
Past attempts to provide wings or wing structures that can be deployed during flight have included traditional wing structures that unfold or swivel out from an envelope within a fuselage portion of the vehicle. Other past attempts include dividing traditional wing structures into folding sub-panels, either spanwise or chordwise, for more volumetrically efficient storage in the space available within the fuselage in the ballistic flight configuration. These wing structures are typically retracted into the fuselage of the vehicle using various pivots, hinges and sliding mechanisms, and generally also require intricate mechanisms for folding, deploying and operating the wing structure. In general, these past attempts often have resulted in wing structures that are complex, have problems with reliability, are expensive, and due to volume constraints in the fuselage these wing structures are limited in the maximum wing surface that they can provide. This latter problem is most evident when relatively low flight speeds are desired.
Relatively low flight speeds generally require larger wing surfaces to provide enough lift to sustain the aerial vehicle's flight. Because of these size requirements, it is often difficult to store these wing structures within the fuselage. When stored, these wing structures generally consume a volume that is the same as or greater than the volume they consume when they are deployed. As the size of the aerial vehicle is reduced, it becomes increasingly difficult and inefficient to store the wing structures within the fuselage.
Since the wing size is limited by the available storage space within the fuselage, these collapsible wing structures generally only support aerial vehicles traveling at relatively high flight speeds. These higher flight speeds result in greater forces acting on the wing structures during flight, however, which in turn increases the structural requirements necessary to support the increased forces acting on the wing structures.
Previous attempts at making folding wings for non-ballistically launched aerial vehicles typically required traditional reinforcing structures such as trusses and spars inside the wing structure, while also using hinges or pinned joints for folding or stowing the wing structure. This often was due to the larger wing area required for a non-ballistic take-off from the ground. In many cases these wing structures were deployed by personnel on the ground using equipment that was not part of the vehicle. The vehicle typically was then activated to take off from a runway like a conventional airplane.
Previous attempts to make collapsible wing structures also have included inflatable wing structures. For strength and stability, however, prior inflatable wings often relied on external brace wires, struts or traditional internal structures, such as trusses and spars. In most of these designs, especially where the additional structures were minimal, the wing surfaces were not truly fair and smooth.
These inflatable wing structures also often were designed with inflatable truss, spar and rib equivalents as substitutes for the non-inflatable structures that they were intended to replace. These inflatable substitutes did not have the same rigidity and stiffness as the non-inflatable components that they were intended to replace, however, and therefore did not perform as well as their conventional stiff wing structure equivalents.
One particular inflatable wing included multiple inflatable spanwise chambers with a soft foam rubber-like material to fill in the spaces between the inflatable chambers and cloth coverings to provide a smooth airfoil surface. Another inflatable wing used helically-wound fibers around rubber tubes that were inflated with several hundred pounds per square inch of pressure. Again, a soft foam rubber-like material provided a smooth airfoil surface. The foam limited the collapsed volume of these wing structures, however. Their deployed versus stowed volume ratios are estimated to be on the order of 4:1 up to 12:1.